Electrochemical energy storage devices are commonly made in two different forms of construction. In one form of construction, the two electrodes are electrically separated from each other by, for example, a synthetic-fiber nonwoven as a separator, and rolled into a spiral coil which is introduced into a cylindrical vessel. The electrodes are connected via specially designed discharge elements or connectors with bushings through the cell wall. After feeding in the requisite amount of electrolyte, thereby filling the system of pores of the electrodes and separator, the cells are sealed.
In the case of prismatic cells, there is a stack of electrodes comprising a multiplicity of individual electrodes which are electrically separated from one another by separators and stacked in an alternating sequence. The positive and negative electrodes are respectively interconnected electrically and connected to corresponding pole bushings through the gastight housing. Such a cell is ready for operation after filling the system of pores of the electrodes and the separator.
Cylindrical cells are often used only for storage units with comparatively low capacities, since in the case of this type of construction it is only possible to increase the capacity by increasing the diameter or extending the height of the cylindrical coil. The first makes it more difficult to dissipate lost heat produced during cyclic operation, while a geometrical extension leaving the capacity of the cell the same results in an increase in the internal resistance or a deterioration in conductivity.
In the case of prismatic cell forms, on the other hand, it is possible for a higher capacity to be achieved without significant sacrifices in the ratio of capacity and conductivity by increasing the cell width with the cell thickness remaining the same. However, one particular advantage of the cylindrical form of construction over prismatic forms of construction is its greater dimensional stability. In particular in the case of water-based battery systems, it is possible for gassing to cause internal pressures to build up when they are under operating pressure. Cells of a prismatic form of construction are sensitive to such compressive stresses and tend to undergo deformations, which are undesired and have to be counteracted by complex design measures.
It is customary to accomplish higher capacities by interconnecting individual cells in parallel. Such connections are carried out both with individual gastight cells and with open cells. An interconnection of individual cylindrical cells makes it possible to accomplish higher capacity values while retaining good dimensional stability. However, this entails greater expenditure, since all the individual cells must be provided with a housing with seals, a valve, current collector, etc. In addition, it is necessary to keep the individual interconnected cells at the same temperature level to ensure a uniform charge acceptance and delivery during continuous operation. Particular difficulties arise if a multiplicity of such storage units created by interconnection are in turn interconnected to form series which have a high system voltage.
Rechargeable batteries with a number of cylindrical cells which are interconnected are disclosed, for example, by DE 19750069 A1. In this case, a temperature-control device is provided between the cells which comprises a hollow body through which a temperature-control medium flows and which has semicircular bulges, the radii of which correspond approximately to those of the cells, and which are arranged in such a way that they fix the spatial positions of the cells in relation to one another.
It would accordingly be advantageous to provide a sealed rechargeable battery which has sets of wound electrodes and in which the advantages of prismatic and cylindrical cells are combined with one another.